1. Field of the Invention
The inventions relate to antennas and microwave transceivers.
2. Description of the Related Art
Conventional antennas often have linear dimensions that are of order of the wavelength of the radiation being received and/or transmitted. As an example a typical radio transmitter uses a dipole antenna whose length is about equal to xc2xd of the wavelength of the waves being transmitted. Such an antenna length provides for efficient coupling between the antenna""s electrical driver and the radiation field.
Nevertheless, antennas whose linear dimensions are of order of the radiation wavelength are not practical in many situations. In particular, cellular telephones and handheld wireless devices are small. Such devices provide limited space for antennas. On the other hand, small antennas couple inefficiently to the radiation at wavelengths often used in cellular telephones and handheld wireless devices.
Various embodiments use antennas that resonantly couple to external radiation at communication frequencies. Due to the resonant coupling, the antennas have high sensitivities to the radiation even if their linear dimensions are much smaller than xc2xd the radiation""s wavelength.
In one aspect, the invention features an apparatus that includes an object and one or more sensors located adjacent to or in the object. The object is formed of a material whose dielectric constant or magnetic permeability has a negative real part at microwave frequencies. The one or more sensors are located adjacent to or in the object and measure an intensity of an electric or a magnetic field therein.
In another aspect, the invention features a method. The method includes exciting an object by receiving microwave radiation and detecting a field intensity internal or adjacent to the object in response to the object being excited by the microwave radiation. The object has either a dielectric constant with a negative real part at microwave frequencies or a magnetic permeability with a negative real part at microwave frequencies.